Introduction: Localization-related epilepsy frequently involves mesial temporal lobe structures (MTLS), but sometimes presurgical workup is confusing since lack of clear structural lesions or inconsistency among multiple tools. We recently improved accuracy of EEG source imaging technique (ESI) and applied it in presurgical epilepsy workup. This study evaluates its contribution to surgical strategy of epilepsy involving MTLS.

Methods: We included patients who underwent resective surgeries encompassing MTLS in this study. In addition to traditional tools, ESI was available in all cases. ESI was accomplished based on 256-channel high-density EEG and individualized finite difference method head models. Patients accepted either one-stage or staged resective surgeries (SEEG implantation+stage-two resective surgeries). Contributions of multiple tools to surgical strategies were evaluated.

Results: Twenty-five cases with Engel I+II outcome after surgeries were included. ESI(80%) and MRI(76.0%) showed higher accuracy over ictal EEG(44.0%) and FDG-PET(56.0%) when defining resective scope as epileptogenic zone(p<0.05). In one-stage cases, ESI showed sources localized within MTLS region in 88.2% (same as MRI positive rate), while PET localized focally only in 64.7% (p<0.05). 62.5% staged cases showed complete concordance of ESI sources with SEEG findings, while for PET & MRI the ratio is 25% & 62.5%, respectively. ESI & PET contributed to SEEG plans in all, while MRI & ictal EEG contributed in 87.5% & 50%, respectively. In subtle lesional/MRI-negative cases, 62.5% showed subtle MRI lesions in MTLS firstly diagnosed as “negative”. ESI contributed more to detection/confirmation of these lesions (75% showed sources confined within MTLS region) than PET estimates (focally-localized in MTLS in 50%) (p<0.05).

Conclusions: Non-invasive accurate ESI method described here is based on high density EEG and individualized head model, appearing contributable to surgical planning of epilepsy surgeries involving MTLS, by indicating MTLS region epileptic sources. This feature can help decide strategy of one-stage resective surgeries and SEEG implantation plans.

Patient Care: By localizing the epileptogenic zone non-invasively, EEG source imaging technique can improve the efficiency of presurgical epilepsy workup, assisting traditional tools. It has features to help detect/confirm subtle/ ambiguous structural lesions in MRI, or even indicate sources in MRI negative cases, in order to help the decision making of one-stage resective surgeries without invasive evaluations. By these features, it can also help in SEEG implantation plan making by indicating epileptic regions including mesial temporal lobe structures.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of EEG source imaging technique as an assistant tool in presurgical workup of intractable localization-related epilepsy involving mesial temporal lobe structures, 2) Discuss the features of this technique with high accuracy based on 256-channel high density EEG as well as individualized head models; 3) Learn the merits as well as pitfalls in using this technique in clinical work.

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